May one rip plastic on shabbos for non-food purposes, such as to open a new pantyhose ?
It is permitted. The reason we are allowed to open certain plastic containers is because it is has a one-time use, and because it is merely ruining the container, and because it is needed for Shabbos. Therefore, a package of pantyhose that is needed to wear for shabbos would be permitted to rip open. It should be opened in a way that ruins the package, and does not rip any words or pictures.
Shmiras Shabbos K’hlilchoso 9 ftnt. 12, Levush O:CH 314-1, Pri Megadim M:Z 413-1, Minchas Yitzchok 4- 82 (5).